Fix bitwise_operations.cc to address return value inconsistency (evangelistalab#378)

* fix bitwise_operations return value inconsistency

* Update forte/sparse_ci/bitwise_operations.hpp

Co-authored-by: fevangelista <[email protected]>

---------

Co-authored-by: marink2 <[email protected]>
Co-authored-by: fevangelista <[email protected]>

Author: 3 people

forte/sparse_ci/bitwise_operations.hpp

@@ -55,7 +55,9 @@ inline double ui64_bit_parity(uint64_t x) { return 1 - 2 * ((std::popcount(x) &
 /// @brief Bit-scan to find next set bit
 /// @param x the uint64_t integer to test
 /// @return the index of the least significant 1-bit of x, or if x is zero, returns ~0
-inline uint64_t ui64_find_lowest_one_bit(uint64_t x) { return std::countr_zero(x); }
+inline uint64_t ui64_find_lowest_one_bit(uint64_t x) { 
+    return (x == 0) ? ~uint64_t(0) : std::countr_zero(x);
+} 
 
 /// @brief Bit-scan to find next set bit after position pos
 /// @param x the uint64_t integer to test